Friday, December 04, 2009

Readers may know that last year, I addressed how carbon nanotube technology had been seeping into the bicycling scene. While by themselves, the properties are very remarkable, the issue we all want to sort out is, how much is the end product we care about - the bicycle frame - improved by using such tech?

Some readers in that article held the view that this technology is an "April Fool's joke" on the consumer, that the change in finished properties in the frame with nanotube reinforcement is extremely small and not worth it considering the increases in cost. Is this just a "feel good" marketing ploy from the cycling industry? Should it have prevented failures such as this one?

Today's article below is borrowed from one of the writings of Dexter Johnson, who is an IEEE technical blogger writing for Nanoclast. Here, he's posing the question of what nanotube reinforced bicycle frames really have to offer in terms of cost-benefit and also explores the different buzz words seen in bicycle marketing literature. Do they mean anything at all?

Enjoy the read and let me know what you think.

Nanotechnology And The Bicycle

Dexter Johnson, IEEESeptember 9, 2009

At a conference that I had put the program together for a few years back, a speaker during his presentation suggested that maybe he would supply some carbon nanotubes to a bicycle manufacturer and have Lance Armstrong ride the bike in the Tour de France. What a great marketing idea, he thought out loud.

Being an avid cyclist and an even more avid fan of cycling, I explained to him that the professional cycling federation had put a weight limit on bicycles and that maybe there was not much to be gained in pursuing this marketing avenue.

How wrong I was. Since then, which I believe was around 2005, I have become aware of at least three high-end bicycles that employ some kind of nanoparticle in the frame.

The three that I know of are Spanish-based BH Bicycles, Swiss-based BMC and most recently I’ve discovered Italian-based Pinarello has gotten on the nano bandwagon.

What does the nanotech actually do for these bikes other than to raise their asking price slightly north of a new economy car? Well, it’s hard to say except by taking a look at their marketing copy.

Let’s start with the BH G4 bike. Here the marketing copy reads: “BH achieves this magical blend of low-weight, great ride and toughness using Nanotechnology resins.”

“Nanotechnology resins”? After reading the rest it appears what they mean is that they are using carbon nanotubes as a filler material between the carbon fibers. Despite the rather breathless description of how carbon nanotubes “have a strength-to-weight ratio orders of magnitude greater than steel”, they never quite get around to saying whether the CNT-enabled resins make the carbon fiber bicycle any stronger or lighter than any other run-of-the-mill resin.

BMC it turns out is using carbon nanotubes in exactly the same way as BH (not really a surprise to be honest). But BMC does manage to say that the material matrix that is developed using these carbon nanotubes is 20% stronger for practically the same weight. I am a little concerned with the usage of the phrase “practically the same weight”. And for that matter what does “stronger” mean?

Pinarello appears to be much more discrete about their foray into nanomaterials, but they do manage to say the following: “the exclusive 60HM1K carbon by Torayca® with Nanoalloy™ that prevents sudden breakage.”

Wow, now we’ve got a nanoalloy (and it’s trademarked)! From what I have been able to piece together about the “Nanoalloy™” from the bicycle trade press is that:

“Nanoalloy… disperses nanoscale elastomers between the carbon fibers. These elastomers have the ability to absorb impacts and prevent the propagation of cracks as they occur.” The result: Pinarello claims the Dogma frame weighs about 860 grams, 40 grams less than the Prince but is 23 percent more resistant to impacts."

Could this resistance to impacts that Pinarello describes be the same “stronger” that BMC offers up?

Is there anything to all of this nano talk in bicycles other than a cool marketing angle? Impossible to say outside of conducting some real experiments, and it’s hard to imagine anyone being that interested to bother.

Now if we can develop a material that would be perfect for the rigors of a bicycle frame by using a material by design method and then build the material and the frame atom-by-atom then I might pay a premium price for it. Will I still be able to ride a bike by then? Stay tuned.

24 comments:

Agree with the article. My sincere opinion is that its better to stay away from any new technology that just appeared recently in the industry. Its costly, haven't proven much in terms of benefits, and the end user is making a gamble by a) not being much knowledgable about what they're getting into, b) opening themselves up to the risk of being the first testee. Save the bucks on something that has taken the rounds and proven something in terms of safety and design. Unless you want to be the pioneer and jump into the unknown waters...

Kono : Thats interesting. I did go and check TIME-Sports website and they label their technology "NANOSTRENGTH". There's absolutely little information on what NANOSTRENGTH actually means The only description of it is :

"To reinforce the matrix of its composite Time has chosen to use nano loads called NANOSTRENGTH developed by ARKEMA. This NANO structure, that binds to the matrix molecules increases the performance criteria for impact and resistance to cracking. The result is even higher performance. "

Yeah, that's the fuzzy marketing speak from Time. There might be some info on http://www.arkema-inc.com/index.cfm?pag=1261 which is Arkema's product page, although what I found there looked rather vague as well. Might be because this isn't really my field, hehe. ;)

Sorry, so I went to the ARKEMA site and here's what how they describe NANOSTRENGTH, apparently its trademarked too :

"Nanostrength® block copolymers are the result of Arkema's unique (meth)acrylates anionic and controlled radical polymerization chemistry and technology. This self-assembling nanotechnology provides benefits to many thermo-set, composite, thermoplastic and rubber applications."

Carbon Nanotubes are all well and good, but I don't think the failure mechanism for bikes is addressed by them. In general, when a carbon frame fails it is not some small crack propagation issue that would have been solved by micro-fibers mixed into the resin. It is rather a catastrophic failure of the resin in compression which leads to complete crumple type failures. Nanotubes do little to address resin/laminate compression strength. I could see fatigue life of a frame increasing from their use, but should we really by using our frames anywhere near their fatigue life?

If crack propagation is the issue, there is something else wrong.

When it comes down to it, carbon has some tensile strength and resin has some compression strength, if you aren't going to improve the compression strength of resins you should focus on structural design like Cervelo seems to do so well.

Any frame manufacturers working in Kevlar for better frame compliance? I'm guessing not because of resin flexibility issues, but I would be curious if anyone has seen it out there?

Ryan : That's exactly the issue here. You can't believe a word mentioned in the marketing literature. So far not a single test has been performed to show that impact strength does increase. Without evidence of improved attributes in bicycle frames, I don't know if I'd believe the hype. In theory though, it does sound good if it wouldn't increase frame weight. But also keep in mind the price can go up three fold.

Energetich : I agree with you on the failure path. Infact, I had written a bit on the on modes of carbon fiber failure here, while checking out someone's broken steerer tube. The OP went through a rough time with his health with something he couldn't see or plan against.

Speaking of testing and such, does anyone know if the German Tour magazine tests for impact? All I have seen so far are tests for torsional head tube stiffness, bottom bracket stiffness, weight and comfort.

The Arkema website does seem like gobbledegook, but I don't think it was written with us as the target reader. On the pdf information sheet the following contact is given, so maybe Robert can explain it to you in less specialised language?

@Ryan : Thanks. From a technical standpoint, again, that PPT presentation you handed us is very basic overview, not anything we didn't know.Literature on specific application in bicycles and a quantification of how strength properties are affected before and after nanotube impregnation is what we need. Not surprisingly, the PPT does make a mention of the huge costs involved in producing nanotubes, leave alone applying them to sports equipment. Cost/benefit ratio does seem to be pretty high.

@Milessio : I have contacted Arkema. Let's see if they tell me anything interesting and different. Thank you for that information.

I understand that "impact resistance" is improved, but what does that mean for the laminate? My understanding is that the tensile strength of the resin itself is improved leading to less microcrack propagation between laminate fibres. It doesn't seem that it would improve the ultimate strength of a frame.

If someone can layup a frame that is lighter, shows the same or better stiffness/compliance characteristics, and fatigue life as other frames using a test bed like Cervelo's(see frame 5 of this slideshow) they should and probably would have. Lacking that testing, I would just fall back to what we know works and is cheaper.

Energetich20, I have to disagree with you strongly about the failure mode of carbon/resin systems. You need to think about it from a micromechanics perspective. "Plain" carbon (no resin) has plenty of compression strength; it's not all that much less than the tensile strength.

However, the fiber diameters are so small that the individual fibers tend to buckle immediately. The resin is there largely to stabilize the carbon, keeping it from buckling under compression.

You suggest that the resin fails in compression; that's not right. Look at the stress/strain curves for the epoxy matrix and the dry carbon; remember that the strain of the fiber must equal the strain of the resin at the fiber/resin boundary. Carbon fibers are so much stiffer than the resin that their stress level at a given strain is much, much higher. When the carbon reaches its ultimate compressive yield strength, the resin hasn't been strained nearly enough to reach its yield stress.

Obviously, once the carbon reinforcement goes, the matrix (with much less strength) fails as well. However, the carbon fibers themselves fail first under a pure compressive load.

Cheers,

Jason

P.S. I saw from your Blogger profile that you're an engineering student at UW-Madison. I got my master's degree there. Which program are you in?

Energetic20, I followed the links in your Blogger profile and I see you're on UW-Madison's concrete canoe team, so you're almost certainly a civil engineering student.

That explains a lot. The compressive failure mode you described is right for reinforced concrete but wrong for carbon/epoxy structures. As you well know, reinforced concrete typically uses steel rods (rebar) to handle tensile loads. Under compression, the concrete bears the load.

Why? Because the concrete matrix is stiffer than steel "fiber". The compressive failure strain for the concrete is much smaller than that of the steel, so the concrete fails first and the steel crumples.

But this is not what happens in a carbon/epoxy laminate. The fiber modulus is typically 10-15 times that of the matrix, so the situation is essentially the opposite of that embodied by reinforced concrete.

At any rate, I now understand why you made your claim about the matrix taking the compressive load and failing first--you were treating carbon/epoxy laminates like reinforce concrete. That's a mistake, but the mistake makes a lot more sense and is very understandable now that I know the context.

Cheers,

Jason

P.S. For what it's worth, I was in the Engineering Physics department at Madison. If you have any interest in learning more about composites in general, I highly recommend Professor Rowlands' class on composites. It's ME 508, so it's technically a mechanical engineering class. However, I'm sure Prof. Rowlands would give you permission to take the class if you were interested. He's a fantastic teacher and a really nice guy; I took 508 from him and then did a semester-long graduate-level independent study project with him. His voice is kind of funny in a good way; it was like learning about composites from Fozzie Bear.

Some subtle points I want to add particularly about carbon fiber failure.

There are multiple modes of failures in composites, its all complex stuff. Matrix cracking, fiber fracture core failure, delamination etc. The thing to realize is that they by themselves need not lead to part failure always. Its often a combination of modes that leads to ultimate failure through propagation through the material.

I don't think anyone has talked about improper layout - if the fiber was not wrapped or formed correctly, a natural break point could easily have been made. The wrong type or amount of resin could have been used, it might not have been vacuum formed correctly, cured at the wrong temperature, presence of impurities etc.

It all depends on the design, and how the laminate is being loaded and subsequent manufacturing schemes.

Thanks for the clarification Jason. The concrete composites are my reference point... I've also got some experience with carbon/kevlar canoes. I still don't see how using nano particles or structures in a resin will help though...

Sorry for responding so late, but I wanted to express my thanks for referencing my blog. I think one of the most satisfying experiences I have had in blogging is actually being referenced by a blog that you admire. Thanks again.